REVENUES FROM CONTRACTS WITH CUSTOMERS (Details) - USD ($) $ in Millions	Apr. 30, 2019	Jan. 31, 2019
REVENUES FROM CONTRACTS WITH CUSTOMERS
Retained amounts by project owners	$ 15.9	$ 15.3

The amounts retained by project owners under construction contracts.

No definition available.

Name:	agx_RetainedAmountUnderConstructionContracts
Namespace Prefix:	agx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant